Abstract:

Understanding microbial adaptation to environmental stressors is crucial for interpreting broader ecological patterns. In the most
extreme hot and cold deserts, cryptic niche communities are thought to play key roles in ecosystem processes and represent excellent
model systems for investigating microbial responses to environmental stressors. However, relatively little is known about the genetic
diversity underlying such functional processes in climatically extreme desert systems. This study presents the first comparative
metagenome analysis of cyanobacteria-dominated hypolithic communities in hot (Namib Desert, Namibia) and cold (Miers Valley,
Antarctica) hyperarid deserts. The most abundant phyla in both hypolith metagenomes were Actinobacteria, Proteobacteria,
Cyanobacteria and Bacteroidetes with Cyanobacteria dominating in Antarctic hypoliths. However, no significant differences between
the twometagenomeswere identified. The Antarctic hypolithicmetagenome displayed a high number of sequences assigned
to sigma factors, replication,recombination andrepair, translation, ribosomal structure,andbiogenesis. In contrast, theNamibDesert
metagenome showed a high abundance of sequences assigned to carbohydrate transport and metabolism. Metagenome data
analysis also revealed significantdivergence inthe geneticdeterminantsof aminoacidandnucleotidemetabolismbetween these two
metagenomes and those of soil from other polar deserts, hot deserts, and non-desert soils. Our results suggest extensive niche
differentiation in hypolithic microbial communities from these two extreme environments and a high genetic capacity for survival
under environmental extremes.